Approximately 10,500-to-17,500-feet (3,200-to-5,350-meters) below the ocean's surface, the researchers saw open fissures in "many places," Tsuji said. They ranged from around 3-to-6-feet (around 1-to-3-meters) across, though the researchers couldn't measure how deep these new cracks extended.
By combining their direct observations with seismic surveys of the seafloor, the researchers uncovered a series of complex faults around the zone where the continental crust off the coast of Japan is being forced under the Pacific tectonic plate. They found when the crust ruptured some 12 miles (20 km) below the planet's surface, it was powerful enough to rip all the way to the surface.
That rupture pushed up a massive amount of seafloor, which in turn triggered the huge tsunami that devastated the coast.
Meanwhile, the wedge of crust where the quake struck was not only thrust outward, but extended horizontally like an accordion, Tsuji reported. That explains the fissures, which occurred as the crust got stretched.